1. Field of the Invention
The present invention generally relates to an ultrasonic diagnosing method and an ultrasonic diagnosing apparatus, capable of transmitting ultrasonic waves to an object to be inspected and receiving ultrasonic echoes reflected from the object so as to display an ultrasonic diagnostic image of the object on the basis of the reflected ultrasonic echoes. More specifically, the present invention is directed to such ultrasonic diagnosing method and apparatus capable of displaying ultrasonic diagnostic images having a better S/N ratio by calculating a correlative coefficient between data which are obtained by detecting ultrasonic echoes reflected from first and second objects.
2. Description of a Related Art
In conventional ultrasonic diagnosing apparatus, ultrasonic transducer elements such as PZT (Pb(lead) zirconate titanate) are employed in order to receive ultrasonic echoes. FIGS. 7A to 7C show waveforms of detection signals which are processed in one conventional ultrasonic diagnosing apparatus. An ultrasonic transducer element which receives ultrasonic waves (ultrasonic echoes) outputs such a detection signal as shown in FIG. 7A. This ultrasonic detection signal is demodulated to obtain such a demodulated signal as shown in FIG. 7B.
Furthermore, since this demodulated signal is filtered by employing a low-pass filter, an envelope signal as shown in FIG. 7C is extracted from the demodulated signal. In this case, an xe2x80x9cenvelopexe2x80x9d implies such a line formed by connecting maximal values of the demodulated signal.
Generally speaking, such an envelope signal is employed as an image signal. However, all components of the detection signal or the demodulated signal are equivalently utilized, so that the image signal obtained in the above-described signal process manner may be easily and adversely influenced by noise.
On the other hand, Japanese patent No. 2676014 (will be also referred to as Document 1 hereinafter) describes the below-mentioned technique. According to the technique, ultrasonic pulse signals transmitted from respective ultrasonic transmitting elements are phase-modulated by using a modulating signal which is constituted in accordance with such an orthogonal function as Walsh function, and correlative coefficients between respective reception waves and a transmission signal are obtained. As a result, it is no longer necessary to scan the interior of the target space. That is, the ultrasonic pulse signals can be transmitted to the interior of this target space at the same time, and therefore, a time duration required to obtain a single ultrasonic image can be considerably shortened.
In accordance with the technique described in Document 1, the time duration required to obtain a single ultrasonic image can be shortened because the interior of the target space is not scanned. However, in such a case where the waveforms of the ultrasonic waves are deformed due to attenuation and scattering phenomena occurred in the ultrasonic wave transmission/reception stages, the correlative coefficients between the respective reception waves and the transmission signal are decreased.
Also, Document 1 discloses the ultrasonic wave transmitting method used in an ultrasonic imaging apparatus. In the ultrasonic wave transmitting method, while pulse-shaped ultrasonic waves are transmitted toward a target space at the same time from a plurality of non-directional ultrasonic-wave transmitting elements arranged in a two-dimensional manner, the scattered waves which are produced by scattering the pulse-shaped ultrasonic waves within the interior of the target space are received by a plurality of non-directional ultrasonic-wave receiving elements. Based upon the signal strengths and also the elapse time from the transmitting operation of this ultrasonic pulse signal to the receiving operation thereof, distribution of the scattering points of ultrasonic waves within the target space is calculated. In accordance with this ultrasonic wave transmitting method, ultrasonic transmission signals are phase-modulated by using modulating signals which are constituted in accordance with orthogonal functions. This phase modulation is carried out by employing the modulating signals which are different from each other for every ultrasonic wave transmitting element. Moreover, while combinations between the phase modulating signals and the ultrasonic wave transmitting elements are changed for every ultrasonic transmitting element, the ultrasonic waves are transmitted plural times in such a time interval during which these ultrasonic waves never interfere with each other. Both the numbers of the ultrasonic wave transmitting elements and the sequential orders of the ultrasonic wave transmissions are converted into binary number indications to obtain exclusive-OR result thereof for every bit. Then, such an ultrasonic wave having an orthogonal function number corresponding to the exclusive-OR result is transmitted from the ultrasonic wave transmitting elements. The distribution of the scattering points can be calculated by receiving the ultrasonic waves plural times.
According to the ultrasonic wave transmitting method used in the ultrasonic imaging apparatus disclosed in the above-described Document 1, while occurrence of an artifact image can be prevented, an ultrasonic image can be obtained in high precision. However, in such a case where the waveforms of the ultrasonic waves are deformed due to s and scattering phenomena occurred in the ultrasonic wave transmission/reception stages, the correlative coefficients between the respective ultrasonic reception waves and the ultrasonic transmission signals are decreased.
The present invention has been made to solve such a problem of the conventional technique. An object of the present invention is therefore to provide ultrasonic diagnosing method and apparatus capable of obtaining an ultrasonic image in high precision even when waveforms of ultrasonic waves are deformed due to attenuation and scattering phenomena occurred in ultrasonic wave transmission/reception stages.
To solve the above-described problem of the prior art, an ultrasonic diagnosing apparatus according to one aspect of the present invention comprises: ultrasonic wave transmitting means for transmitting ultrasonic waves each having a predetermined waveform; ultrasonic wave receiving means for receiving ultrasonic echoes reflected from an object to be inspected to thereby output detection signals; signal processing means for processing the detection signals derived from the ultrasonic wave receiving means to thereby produce data; first storage means for storing data which is obtained by transmitting ultrasonic waves to a first object and receiving ultrasonic echoes reflected from the first object; second storage means for storing data which is obtained by transmitting ultrasonic waves to a second object and receiving ultrasonic echoes reflected from the second object; correlative coefficient calculating means for calculating a correlative coefficient between the data stored in the first storage means and the data stored in the second storage means; image processing means for producing an image signal based upon the correlative coefficient calculated by the correlative coefficient calculating means; and an image display unit for displaying an ultrasonic diagnostic image based upon the image signal produced by the image processing means.
Also, an ultrasonic diagnosing method according to one aspect of the present invention comprises the steps of: (a) storing data which is obtained by transmitting ultrasonic waves each having a predetermined waveform to a first object and receiving ultrasonic echoes reflected from the first object; (b) storing data which is obtained by transmitting ultrasonic waves each having a predetermined waveform to a second object and receiving ultrasonic echoes reflected from the second object; (c) calculating a correlative coefficient between the data stored at step (a) and the data stored at step (b); (d) producing an image signal based upon the correlative coefficient calculated at step (c); and (e) displaying an ultrasonic diagnostic image based upon the image signal produced at step (d).
As a consequence, according to the ultrasonic diagnosing method/apparatus of the present invention, the correlative coefficient between the data obtained by detecting ultrasonic echoes reflected from the first object and the data obtained by detecting ultrasonic echoes reflected from the second object is calculated, so that the ultrasonic image signals may not be easily nor adversely influenced by the noise. As a consequence, even in the case where the ultrasonic waves are attenuated or scattered, the large correlative coefficients can be obtained, so that the ultrasonic images having the superior S/N ratios can be obtained.